Stimuli and response- BP

Question 1

What is a Stimuli?

Answer 1

a change in the internal or external environment

Question 2

Why do Organisms need to Respond to Stimuli?

Answer 2

for survival (predator/prey awareness, homeostasis)

Question 3

How do Simple Organisms Respond to Stimuli?

Answer 3

Taxis and Kinesis

Question 4

What is Taxis?

Answer 4

directional response to a stimuli (towards or away from)

Question 5

What is Kinesis?

Answer 5

 non-directional movement from an unfavourable area to a favourable area
 organism moves rapidly and randomly in unfavourable area until they reach favourable area where they move slowly and less randomly
 so spends more time in favourable area, less time in unfavourable area

Question 6

Example of Response to Stimuli in Plants?

Answer 6

Tropism

Question 7

What is Tropism?

Answer 7

 directional growth in plants in response to a stimuli
 towards = positive, away = negative
 light = photo, water = hydro, gravity = geo
 shoot shows positive phototropism and negative geotropism
 root shows positive geotropism and positive hydrotropism
 controlled by a Plant Growth Factor = Indoleacetic Acid (IAA) - auxin

Question 8

What is a Plant Growth Factor?

Answer 8

equivalent to animal hormones

Question 9

What are the affects of IAA?

Answer 9

• promotes growth in the shoot
• inhibits growth in the root

Question 10

How does positive phototropism in the shoot take place?

Answer 10

 normally: shoot tip produces IAA, sending it down both sides causing the shoot to grow forwards
 if light is present on one side, the IAA redistributes to the opposite side (shaded side)
 this causes the opposite side to grow faster
 so the shoot bends towards the light

Question 11

How does negative geotropism in the shoot take place?

Answer 11

 if gravity is present on one side, the IAA redistributes to the same side
 this causes the same side to grow faster
 so the shoot bends away from gravity towards the light

Question 12

How does positive geotropism/hydrotropism in the root take place?

Answer 12

 if gravity/water is present on one side, the IAA redistributes to the same side
 this causes the same side to grow slowly, so the opposite side grows faster
 so the root bends towards the gravity/water

Question 13

Evidences for Tropism (positive phototropism in shoot)?

Answer 13

• removing or covering shoot tip prevents tropism [tip causes tropism]
• placing micin (prevents movement of chemicals e.g. IAA) across shoot inhibits tropism [tropism caused by movement of chemicals]
• placing gelatine (prevents movement of electrical signals) across shoot does not affect tropism [tropism not caused by movement of electrical signals]
• if shoot tip is moved to one side, that side grows faster and the shoot bends the other way [IAA promotes growth in shoot]
• when in light or darkness the overall levels of IAA remain the same [light does not inhibit or breakdown IAA but rather redistributes it]

Question 14

Response to Stimuli in Mammals?

Answer 14

uses Nervous System, Hormonal System (nervous and hormonal systems coordinate response to stimuli)

Question 15

Job of Nervous System?

Answer 15

• coordinate response to certain stimuli
• response is fast, short acting, localised

Question 16

Pathway of Nervous System?

Answer 16

stimuli to receptor to sensory neurone to spinal cord to brain to spinal cord to motor neurone to effector for response

Question 17

What does a Receptor do?

Answer 17

 detects stimuli & converts stimuli energy into nerve impulse (acts as a transducer – converts one type of energy into another)
 each type of stimuli has a specific receptor
 uses stimuli energy to send Na+ ions into the start of the sensory neurone
 2 examples of receptors: Pacinian Corpuscle, Retina of Eye

Question 18

What does a Pacinian Corpuscle do?

Answer 18

 touch receptor
 found in skin, fingers and toes
 responds to pressure/touch

Question 19

How does the Retina of the Eye work?

Answer 19

 detects light so the brain can generate an image
 detected by retina (located at back of eye)
 made of Cone and Rod cells

Question 20

Properties of Cone Cells in Retina?

Answer 20

 made of Iodopsin Pirgment which is only broken down at high light intensity
 one cone cell connects to one bipolar neurone which connects to one sensory neurone (therefore no summation of light can take place so only detects high light intensity)
 but because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli can be distinguished = high visual acuity

Question 21

Properties of Rod Cells in Retina?

Answer 21

 made of Rhodopsin Pigment which can be broken down at low light intensity
 a few rod cells connect to one bipolar neurone which connects to one sensory neurone (therefore summation of light can take place so can detect low light intensity)
 but because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, the stimuli will be merged together = low visual acuity

Question 22

What is the Central Nervous System (CNS)?

Answer 22

 made of brain and spinal cord
 brain = analyses and coordinates response to stimuli
 spinal cord = connects brain to sensory and motor neurones

Question 23

What is the Peripheral Nervous System (PNS)?

Answer 23

 made of the sensory and motor neurone
 a neurone transmits a nerve impulse
 sensory neurone takes nerve impulse from receptor to CNS
 motor neurone takes nerve impulse from CNS to effector
 sensory neurone has its cell body in the middle and has a dendron and axon
 motor neurone has its cell body at the start and only has a long axon

Question 24

What are the 2 different types of Motor Neurone?

Answer 24

 Voluntary (Somatic) and Involuntary (Autonomic) Motor Neurones
 Somatic supplies skeletal muscle = under conscious control
 Autonomic supplies cardiac muscle, smooth muscle, glands = under subconscious control
 Autonomic can be divided into Sympathetic and Parasympathetic (have opposite effects)

Question 25

What is a Nerve Impulse?

Answer 25

 movement of an action potential along a neurone  action potential = change in membrane potential (charge' in one section of the neurone  changes from negative (polarised) to positive (depolarised) back to negative (repolarised/ hyperpolarised)

Question 26

What is Resting Potential?

Answer 26

 membrane potential of neurone at rest  is -65mV  polarised  caused by having more positive ions outside neurone compared to inside  involves Na+/K+ pump, pumping 3 Na+ ions out, 2 K+ ions in  K+ channel allowing K+ ions to diffuse out (K+ ions will eventually stop diffusing out due to a positive potential outside)

Question 27

What happens during an Action Potential?

Answer 27

 stimuli causes Na+ ions to enter the start of the neurone  makes membrane potential less negative  if it reaches threshold (-50mV), Na+ channels open  therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)  the membrane potential reaches +40mV  then the Na+ channels close, the K+ channels open  therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)  too many K+ ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)  one action potential = depolarisation, repolarisation, hyperpolarisation

Question 28

How does an Action Potential move along a Neurone?

Answer 28

- by local currents - if the stimuli energy is large enough and enough Na+ ions enter the start of the neurone, threshold will be reached and an AP will occur (the 1st AP is called a Generator Potential) - Na+ ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach threshold and an AP to occur - this process continues along the neurone * an AP will always move along the neurone to the end

Question 29

why does AP not move back?

Answer 29

- previous section has just finished an AP - therefore it is in refractory period - Na+ channels cannot be opened - it is hyperpolarised - therefore threshold cannot be reached

Question 30

How does the Size of Stimuli affect a Nerve Impulse?

Answer 30

- does not affect size of AP (AP is all or nothing - reach threshold = get AP [all] - do not reach threshold = no AP [nothing]) - larger stimuli increases the frequency (number) of APs

Question 31

What affects Speed of Nerve Impulse?

Answer 31

- temperature = higher temp, higher kinetic energy, faster rate of diffusion of ions (faster nerve impulse) - axon diameter = wider diameter, neurone less leaky (faster nerve impulse) - myelination = schwann cells wrap around axon, insulates axon preventing AP, therefore AP only occurs in gaps – called node of ranvier, so AP jumps from node to node = saltatory conduction (faster nerve impulse)

Question 32

What is a Synapse?

Answer 32

 connection between 2 different neurones  sends nerve impulse across the gap (synaptic cleft) using neurotransmitters (e.g. acetylcholine)

Question 33

What are the Properties of Synapses?

Answer 33

- unidirectionality = AP/nerve impulse travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors - filters out low level stimuli = low level stimuli do not release enough neurotransmitter, therefore not enough Na+ ion channels open, therefore not enough Na+ ions enter postsynaptic neurone for threshold to be reached, therefore no AP produced - summation = low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial - inhibitory = normal synapses are excitatory (cause AP), some can be inhibitory – prevent action potential from occurring by making postsynaptic neurone hyperpolarised

Question 34

what are the two types of summation?

Answer 34

temporal spatial

Question 35

What is a Reflex?

Answer 35

- a rapid involuntary response to a stimuli - does not use the brain - the sensory neurone connects directly to motor neurone (stimuli to receptor to sensory neurone to relay neurone to motor neurone to effector for response) - ensures less damage done and does not require learning

Question 36

How is Heart Rate controlled?

Answer 36

 the heart is myogenic, its heart beat is initiated by the SAN  the Medulla Oblongata in the brain can increase or decrease heart rate  receives nerve impulse from chemoreceptors (respond to blood pH) in the carotid arteries and pressure receptors (respond to blood pressure) in the carotid arteries and aorta  sends impulse in sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR

Question 37

How does Exercise affect Heart Rate?

Answer 37

 exercise = muscle contraction, which requires respiration  therefore, waste product CO2 is released into blood  this lower pH of blood (acidic)  this is detected by chemoreceptors in carotid arteries  sends impulses to medulla oblongata  then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase  benefit = increase blood flow to lungs to remove CO2 and take in O2

Question 38

How does Low Blood Pressure affect Heart Rate?

Answer 38

 if a person moves from lying/sitting to standing, blood pressure falls (reducing blood flow to the brain)  this is detected by pressure receptors in the carotid arteries and aorta  sends impulses to medulla oblongata  then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase  benefit = increasing heart rate leads to an increase in blood pressure (so enough blood can reach the brain)

Question 39

how does a synapse transmit nerve impulses between 2 neurones?

Answer 39

 AP arrives in end of presynaptic neurone  Ca2+ channels open  Ca2+ ions enter presynaptic neurone  causes vesicles containing neurotransmitter to move to presynaptic membrane  vesicle binds to membrane releasing neurotransmitter into cleft  neurotransmitter diffuses across cleft  binds to complementary receptors on postsynaptic membrane  Na+ channels open, Na+ ions enter  if threshold is reached, AP occurs

Question 40

structure of pacinian corpuscule?

Answer 40

structure = corpuscle (several layers of tissue) wrapped around the start of a sensory neurone

Question 41

process of pacinian corpuscle?

Answer 41

- pressure applied - corpuscle compressed - stretch-mediated Na+ channels opened - Na+ ions move into the start of the sensory neurone

Question 42

cone vs rod cells?

Answer 42

 Cone Cells detect high light intensity only, produces colour image, with high visual acuity  Rod Cells can detect low light intensity, produces black and white image, with low visual acuity  Cone Cells located in centre of retina (fovea) – site of high light intensity  Rod Cells located in periphery of retina

Question 43

how does synapse return to rest?

Answer 43

- enzyme used to breakdown neurotransmitter, e.g. acetylcholinesterase - breaks down acetylcholine into ethanoic acid and choline - diffuses back into presynaptic neurone - ATP used to reform neurotransmitter into vesicle and actively transport Ca2+ ions out

Question 44

difference between plant growth factor and human hormone?

Answer 44

- made by cells throughout the plant - only affects cells locally - affects growth

Question 45

what is spatial summation?

Answer 45

a low level stimuli from a few presynaptic neurones add together

Question 46

what is temporal summation?

Answer 46

low level stimuli present for extended period of time

Question 47

what are the 3 main purposes of a refractory period?

Answer 47

- AP propagated in one direction only - impulses produced are discrete - limits the number of action potentials

Question 48

saltatory conduction?

Answer 48

propagation of a nerve impulse along myelinated axon in which the AP jumps from one node of ranvier to another